There is known a drum brake apparatus having a dual mode structure which, in service braking, by operating a hydraulic cylinder device, operates as a leading trailing (LT) type drum brake apparatus and, in parking braking, by operating a parking brake lever, operates as a duo servo (DS) type drum brake apparatus (see the patent document 1).
A dual mode drum brake apparatus 501 of this type shown in FIG. 15 includes a pair of first and second shoes 503 and 505 disposed opposed to each other on the inner peripheral surface of a brake drum (not shown). The first and second shoes 503 and 505 are elastically supported on a backing plate 511 by first and second shoe hold devices 507 and 509 such that they are movable relative to each other within a limited range. They are also elastically energized in their mutually approaching directions by a pair of first and second return springs 513 and 515. The adjoining ends of the first and second shoes 503 and 505 existing downward in FIG. 15 are respectively contacted with an anchor 517 fixed to the backing plate 511. The adjoining ends of the first and second shoes 503 and 505 existing upward in FIG. 15 can be pressed respectively by the first and second pistons 521 and 523 of a wheel cylinder 519 serving as a hydraulic actuator mounted on the backing plate 511, whereby the first and second shoes 503 and 505 can be expanded.
On the end side of the second shoe 505 existing near the wheel cylinder 519, a forward-pull type first parking brake lever 529 is pivotally supported on a second web 525 through a pin 527. The first parking brake lever 529 constituting this mechanical actuator (expansion mechanism) is rotatable within a plane perpendicular to the axis of the drum. To the free end 531 of the first parking brake lever 529, there is connected a parking brake cable (not shown). When the parking brake cable is pulled by a parking brake operation force, the free end 531 of the first parking brake lever 529 is displaced in a direction shown by W. Thus, the first parking lever 529 can be rotated around the pin 527 in its corresponding direction.
On the one hand, for expanding the second shoe 505 through the pin 527 around its contact point with the anchor 517 and, on the other hand, for rotating a second parking brake lever 535 through a strut 533 clockwise around a projection 537, the first parking brake lever 529 constitutes an expansion mechanism for expanding the first shoe 503 through the projection 537 around its contact point with the anchor 517.
The ends of the first and second shoes 503 and 505 existing backward in the drum rotation direction are dragged by the brake drum and the drum rotation force is transmitted through the strut 533 to the first and second shoes 503 and 505 and is received by the anchor 517, whereby, in parking braking, the dual-mode drum brake apparatus 501 operates as a duo-servo type drum brake.